The present invention relates generally to improvements in fuel systems for turbofan jet engines, and more particularly to a novel system and method for draining excess fuel from the fuel pump of a jet engine afterburner following augmentor shutdown to prevent sudden dumping of the excess fuel.
During flight testing of a conventional jet aircraft powered by an augmented turbofan jet engine, it was reported that the aircraft would leave a large white puff of vapor during deceleration from augmented flight to nonaugmented flight. The puff was reported to be quite large and disclosed the position of the aircraft to both ground and air observation. It was determined that this presents an unacceptable hazard for operation of the aircraft within any potentially hostile environment.
In the operation of a jet engine afterburner, the fuel pressure is reduced in the augmenter fuel pump after augmented operation is terminated, and a vent valve on the pump is opened to allow the excess fuel in the augmenter pump to drain out for jettisoning overboard of the aircraft. In existing systems, most of the excess fuel is drained overboard in less than one second, which generates a white puff of vapor as a short vapor trail. Existing systems include the use of drain cans attached to the engine for collection of the excess fuel from the augmenter fuel pump; the cans are unacceptably large and heavy for many applications. Another system includes piping the excess fuel from the pump and back to the exhaust gas. This arrangement does not solve the vapor problem because the ejected fuel cools and becomes a white vapor trail two to three aircraft lengths behind the aircraft.
The present invention substantially eliminates the white vapor characteristic of augmenter fuel pump venting in conventional turbofan jet engines. The augmenter fuel pump drain system of the present invention may be applicable to all existing augmented turbofan jet engines.
It is, therefore, a principal object of the present invention to provide a novel system and method for venting excess fuel from the augmenter pump of a turbofan jet engine following augmenter shutdown.
It is a further object of the present invention to improve stealthiness of a jet aircraft by substantially eliminating visible vapor occurring upon dumping of excess fuel from the augmenter fuel pump.
These and other objects of the present invention will become apparent as the detailed description of certain representative embodiments thereof proceeds.